The present invention relates to a magnetic bearing device for supporting a main shaft of a working machine in a non-contact manner and a magnetic bearing spindle device.
Conventionally, in a working machine such as a grinding device, a cutting device, a machining center, for high-speed rotation of a main shaft, a magnetic bearing spindle device for supporting a main shaft (spindle) by a magnetic bearing in a non-contact manner has been widely used. In such a magnetic bearing spindle device, for example, as shown in JP-A-H10-29101, the spindle is generally supported by one set of axial magnetic bearings and two sets of radial magnetic bearings in the non-contact manner.
In the above-described magnetic bearing spindle device, it is necessary to detect a bearing load of the magnetic bearing in order to perform abnormal diagnosis. A method of detecting the bearing load includes, for example, a method of using a piezoelectric force sensor. That is, as shown in FIG. 7, a work 51 is supported by a shoe (supportable jig) 52 including the piezoelectric force sensor therein. The force sensor converts force, which acts on the shoe 52 through the work 51 when the work 51 is machined by a machining tool 53, into an electric signal and outputs the converted electric signal as a detection signal of the force received by the work 51. A control device such as a microcomputer obtains the force received by the work 51 as the bearing load on the basis of the detection signal from the force sensor. This method is frequently employed even in a rolling spindle device using a rolling bearing such as a ball bearing as supporting means of the main shaft. However, since the above-described piezoelectric force sensor is generally expensive, it is necessary to obtain the bearing load of the magnetic bearing without using the force sensor, in view of the cost of a product.
Accordingly, as the method of detecting the bearing load without using the force sensor, the load which acts on the magnetic bearing on the basis of current supplied to an electromagnet configuring the magnetic bearing may be obtained. However, in this case, since a relationship between the current supplied to the magnet and attraction force of the magnet is non-linear, a complicated calculation is necessary for obtaining the bearing load of the magnetic bearing on the basis of the current supplied to the magnet. Accordingly, as shown in FIG. 8, the control device 61 of the magnetic bearing includes a board computer 66 for calculating the bearing load of the magnetic bearing on the basis of the current supplied to the magnet 64 through an amplifier 65, in addition to a programmable logic controller (PLC) 63 for controlling a rising position of a main shaft 62 through the control of the supply of power to the magnet 64. The employment of the board computer is not preferred from the viewpoint of the cost of the product. However, since it is difficult to perform the complicated calculation for obtaining the bearing load in the PLC 63, the board computer 66 should be employed. Accordingly, as the configuration of the control device 61 becomes complicated, it is impossible to reduce the cost of the product.